Thermal Barrier Coatings (TBCs) are used extensively in aircraft, marine and industrial gas turbine engines and in some diesel engines. They typically consist of a single metallic (or intermetallic) bond coat and a single ceramic top coat. The bond coat is made from a high aluminum content alloy such as NiAl modified with platinum and/or rare earth elements or a NiCoCrAlY alloy is used to provide oxidation and hot corrosion protection of the substrate (which is usually a nickel or cobalt based superalloy) and to promote the growth of an alpha aluminum oxide thermally grown oxide (TGO) which has high adhesion to the bond growth and provides a stable surface for the top coats deposition. The top coat typically consists of yttria stabilized zirconia (YSZ) (typically 7-8 wt. % yttria with the balance zirconia). It provides thermal insulation of the underlying metal. By insulating the metallic component, its temperature is reduced allowing it to last longer or to survive with less cooling air (cooling air reduces the performance of the engine). Spallation, foreign object damage, hot corrosion and glassy contaminants limit the average coating life and preclude the use of these coatings in prime reliant applications where failure of the coating would result in failure of the components it is applied to.